[woodruffw]

In most countries that's called "forgery." You can't pass of someone's signature, even if it's authentic, in a context they did not intend.

(It should be obvious why it's illegal, and what's wrong with it -- nobody wants bank accounts opened in their name by unrelated parties. You should then be able to reason by parallel as to why it's not a desirable property in a cryptosystem.)

[upofadown]

>...nobody wants bank accounts opened in their name by unrelated parties.

How could you possibly open a bank account with someone's random signed document? A signature on paper identifies who signed it. That is the point. So a bank receiving a paper or PGP message that says "Please open an account" signed by Bob is somehow going to end up opening an account for someone else?

I think you might of gotten the "surreptitious forwarding" issue backwards. The issue is that you might think a signed message is to you when it was actually sent to someone malicious who then forwards it on to you. My point is that this issue is already well understood in our present civilization and doesn't need some sort of technical fix.

For the bank example, the bank you sent your strangely generic request for an account to would have to take that request and send it to another bank. So now you would end up with two accounts and on trivial investigation would know exactly what happened.

Bringing this back to age, the bank would get an unsigned request for an account and would have no way to know who originated it.

Related: https://articles.59.ca/doku.php?id=pgpfan:forwarding

[woodruffw]

> How could you possibly open a bank account with someone's random signed document? A signature on paper identifies who signed it. That is the point.

The normal examples are surreptition and impersonation:

* I could include your bank statement in the stack of physical documents reviewed for a new account. An overworked banker might miss the different name, or different signature, and treat it as another legitimate item for me when it’s a legitimate item for you. After all, it’s signed and legitimate looking.

* More interestingly, I can just pretend to be you. If you don’t already have an account with the bank, I can give them my phone number and address instead. I have your signed document!

The latter is how a lot of account fraud actually happens, and maps to PGP’s failure to provide strong identity through the “web of trust.” See, for example, people “verifying” email signatures by just looking the “right” key up on a keyserver.

[upofadown]

How does any of this relate directly to the issue of "surreptitious forwarding"? What does the web of trust have to do with anything?

[tbrownaw]

How exactly is it forgery for someone's landlord to send a copy of their (signed) lease to the local paper?

[woodruffw]

Emphasis on “pass off”: it’s not forgery to present the original document for its original purpose. It would be forgery to modify the document or to present it in a way or context that implied some other purpose.